dwightlooi

But doesn't DOHC allow for more options with VVT and VVL?

The easy way to put it is that DOHC allows for more "convenient" implementations of VVT and VVL.

When it comes to VVT, because a Pushrod or SOHC engine uses a single cam to operate both the intake and exhaust valves, varying the phasing of that cam advances or retards both in unison. This is called "synchronous" VVT-- the L99 and LT1 engines use this scheme. This is the common and most "straight forward" design, but benefits are not as great as systems able to vary the intake and exhaust timings independently. However, SOHC and pushrod designs can implement cam-in-cam independent VVT (ala Dodge Viper's 8.4 V10) and achieve the same benefits.

When it comes to VVL, there is really no advantage or disadvantage either way. Systems that use locking/unlocking lifters or followers can be implemented on SOHC or DOHC or Pushrod designs with similar ease. The simplest will be the design used on Jaguars and Porsches, which basically have concentric lifters which locks an unlocks (see below). Systems using an eccentric shaft (eg. BMW's valvetronic or Nissan's EOVVL) can also be implemented either way. In fact, the systems become less complex and less costly if you have less valves (ie. 2-valves vs 4-valves).

As you can see, you can use a concentric lifter to operate the valve stem or a pushrod. It really doesn't matter.

The three facts which many people fail to recognize is that...

High Specific Output does not translate to Better Fuel Economy. In fact, many of the design choices made to achieve high specific outputs reduce fuel economy. Let me give you a few examples. A 4-valve or 5-valve cylinder head with two cams per cylinder bank allows greater valve area and lower actuated valve-train mass. This gives you better breathing potential at high RPM, wide open throttle, conditions. But, what you think has more friction? One camshaft or four? One sprocket or four? 12 valves, 24 valves or 30 valves? The answer is obvious, more stuff rubbing together creates more friction -- friction which must be overcome by energy produced by burning fuel, hence it hurts fuel economy. Some people mistakenly reason that better breathing potential reduces pumping losses which offsets the greater friction. This is absolutely untrue except when the throttle is fully open -- which is not how EPA mpg tests are conducted or how most people drive their cars 99% of the time. Anytime the pedal is not all the way to the metal, the breathing of the engine is constricted by the throttle butterfly not the intake valves. Another way to achieve high specific output is through supercharging or turbocharging. Superchargers force feeds the engine with more air by driving an air pump with power produced by the engine consuming additional fuel. Turbochargers do it with relatively "free" energy otherwise wasted through the exhaust -- although they do hurt aspirational efficiencies somewhat by imposing a requisite increase in exhaust back pressure. However, both systems, in order to allow the engine to operate on compressed air without pinging or knocking, also reduces the compression ratio. This hurts fuel efficiency at cruise and anything but wide open throttle scenarios by reducing effective charge density when the engine is not in boost or not in full boost -- which is most of the time. DOHC multi-valve design, superchargers and/or turbochargers also add mass and bulk to the powerplant. All of which increase the dead weight the vehicle lugs around hurting fuel economy. It's very simple really, at any given displacement a DOHC multivalve engine, supercharged engine or turbocharged engine is less fuel efficient than an SOHC 2-valve or pushrod engine that is normally aspirated. The latter will make less power, but it will be more fuel efficient.

While High Specific Output allows lower displacement engines to be used to satisfy a given performance requirement, that smaller displacement engine is not necessarily lighter or more compact. Dual cam heads are taller, wider and heavier. In many instances, a dual cam engine is about the same weight and exterior dimensions as a SOHC or pushrod engine roughly 25~50% greater in displacement. This is especially so with Vee type engines. A 436hp LS3 pushrod 6.2 liter V8 from the last generation Corvette weighs 183 kg vs 202 kg for a 414hp DOHC 4.0 liter S65 V8 in a BMW M3 (both engines having port injection and aluminum blocks). Turbochargers add weight, and their required accessories like intercoolers, bypass valves, pipings and the like add even more. A twin turbocharged V6 like the VR38DETT in the Nissan GT-R -- arguably one of the best of its breed -- makes an impressive 520 hp from 3.8 liters and six cylinders. But it weighs 276 kg. A similarly powerful (505 hp) pushrod V8 like the 7.0 liter LS7 from the 6th Gen Corvette Z06 or the new Camaro Z28 weighs 206 kg. Let's forget high power engines for a second and look at run of the mill four cylinder powerplants from the same manufacturer. A Saturn 1.9L SOHC 8-valve engine weighs 89 kg whereas the DOHC version of the same displacement (same block actually) weighs 100 kg. If you are wondering, Honda -- the company that makes 125 bhp/liter 9,000 rpm S2000s -- chooses a SOHC 2-valve per cylinder design for the current Insight Hybrid for better efficiency than a comparable DOHC engine of similar output.

Some of the design choices you can make that has the most benefit to fuel economy specifically trades Specific Output for reduced Specific Fuel Consumption. The best example of this is the use of the pseudo Atkinson cam grind. Such a cam grind intentionally extends the opening duration of the intake valves well into the compression stroke. This allows air to be kicked back out the cylinders as the piston goes up and negated compression for the first 20~30% of the intake stroke. Because the power stroke is the not reduced the expansion ratio of the engine is effectively lengthened and the energy recovery is significantly enhanced. The engine is 20~33% less powerful, but about 10~15% more fuel efficient. The Prius and Fusion Hybrid (most hybrids for that matter) use a Pseudo Atkinson engine. Another classic trick to improve fuel economy at the expense of specific output is the deliberate use of narrow intake tracts and/or small or asymmetric intake valve openings. The smaller the office and the narrower the tract, the higher the air velocity at any given mass air flow rate. This translates to greater swill and/or tumbling action inside the cylinders which leads to better fuel-air mixing and more even and complete combustion. This dates back to the 1976 Honda Civic CVCC and though supplanted to some degree with the reliance on high injection pressures and direct atomization in today's newest DI engines, this technique is still beneficial enough that some manufacturers (Honda and Jaguar comes to mind) which uses a cam switching system to enable a very low lift valve at lower engine speeds to improve economy.

So... when somebody says this engine is more efficient because it makes more horsepower per liter, think again! And, if moronic legislators push displacement taxes as a means to reduce fuel consumption, carbon foot print and/or energy dependence, maybe you shouldn't vote for them!

Awesome Post Dwight, thanks for sharing this standardization of engines. This totally makes sense for a Global platform with minimal cost to meet the the needs of the market place.

My question for you, if you had to do this same list for CNG and Diesel, what would it look like?

CNG engines are basically the same as the gasoline engines, except that you need bulky tanks and you can use a lot more compression. Or you can run them at the gasoline compression levels and not reap the full benefits. So, basically, you'll swap pistons for pent roof pistons to bring compression to about 14~15:1.

Diesels can be simply six engines. Four low displacement, high specific output diesels for the European market which is largely displacement tax hampered. Two heavy Pushrod 4-valve / cylinder Duramax engines heavy duty vehicles. The four CDTi diesels, share pistons, rods, valves and most internals. In fact, the 6 and 8 cylinder engines are basically two banks of the 3 and 4 cylinder powerplants, sharing the same turbo and aftercoolers amongst other things. Likewise the Duramax engines are internally identical except for the number of cylinders, with the V6 having a single balance shaft for harmonics reductions and the V8 having none.

• (D1) Heavy Duty Trucks / Vans / SUVs / Buses / Limousines -- V8 Duramax Turbo, #2 Diesel, DI, 6599 cc -- 400 bhp @ 3000 rpm / 770 lb-ft @ 1600 rpm*
• (D2) Heavy Duty Trucks / Vans / SUVs / Buses / Limousines -- V6 Duramax Turbo, #2 Diesel, DI, 4949 cc -- 300 bhp @ 3000 rpm / 575 lb-ft @ 1600 rpm

• (E1) High Performance European Cars -- V8 CDTi Bi-Turbo, #2 Diesel, VVT, DI, 3196 cc -- 272 bhp @ 4200 rpm / 472 lb-ft @ 2100 rpm
• (E2) Performance European Cars -- V6 CDTi Bi-Turbo, #2 Diesel, VVT, DI, 2497 cc -- 200 bhp @ 4000 rpm / 350 lb-ft @ 2000 rpm
• (E3) Economy European Cars -- I4 CDTi Turbo, #2 Diesel, VVT, DI, 1598 cc -- 136 bhp @ 4200 rpm / 236 lb-ft @ 2000 rpm*
• (E4) Ultra Economy European Cars / Diesel-Electric Hybrids -- I3 CDTi Turbo, #2 Diesel, VVT, DI, 1199 cc -- 100 bhp @ 4000 rpm / 175 lb-ft @ 2000 rpm

* Existing Engines

The E-series is intended to maximize tax benefits in the EU by using the highest specific output configuration as well as diesel fuel. The E-series also offer more cylinders and greater refinement compared to the competition. Whereas the typical BMW or MB diesel in the 250~300 hp class is a V6, the E-series uses 8 cylinders. Whereas the typical 140 hp four cylinder diesel in Europe is a 2.0L, the CDTi is a 1.6. The Duramax 6.6 is already a very successful product. Instead of the stillborn 310hp 4.5L DOHC 72 degree V8 for lighter duty commercial vehicles and trucks, the Duramax 5.0 V6 picks up that role using a cut down Duramax 6.6 reverse flow block offering essentially the same output using 0.5 liters more displacement but 2 fewer cylinders.

Honestly, I am not a big fan of GM doing the 4.3 V6 and 5.3 V8s. To keep logistics, tooling and development costs to the minimum, all pushrod engines should use the same bore x stroke dimensions and share internals. By standardizing on 103.25 x 92 mm cylinders, they will still have a sufficient spread of power power levels for relevant applications:-

• (C1) Super Cars -- V8 Supercharged, 91 Octane, VVT, DI, VVL, 6162 cc -- 700 bhp @ 6800 rpm / 650 lb-ft @ 3800 rpm
• (C2) Maximum Performance Cars -- V8, 91 Octane, VVT, DI, 8/4 AFM, 6162 cc -- 460 bhp @ 6000 rpm / 465 lb-ft @ 4600 rpm
• (C3) Performance Cars -- V6, 91 Octane, VVT, DI, 6/3 AFM, 4622 cc -- 345 bhp @ 6000 rpm / 350 lb-ft @ 4600 rpm
• (C4) Sport Compact (RWD) -- V4 Supercharged, 91 Octane, VVT, DI, VVL, 3081 cc -- 300 bhp @ 6000 / 300 lb-ft @ 2600 rpm

• (T1) Heavy Duty Trucks / Vans / SUVs -- V8, 87 Octane, VVT, DI, 8/4 AFM, 6162 cc -- 420 bhp @ 5200 / 440 lb-ft @ 2800 rpm
• (T2) Medium Duty Trucks / Vans / SUVs -- V6, 87 Octane, VVT, DI, 6/3 AFM, 4622 cc -- 315 bhp @ 5200 / 330 lb-ft @ 2800 rpm
• (T3) Light Duty Trucks / Van / SUVs -- V4, 87 Octane, VVT, DI, 3081 cc -- 210 bhp @ 5200 / 220 lb-ft @ 2800 rpm

This covers everything you don't want a DOHC I4 or DOHC V6 in the engine bay. There can be some cross population of course... for instance, the base engine for a RWD Sport Compact may use the (T3) 210 hp normally aspirated V4, similarly a Police Caprice may be given the (T1) truck V8 instead of the (C2) Performance Car V8 in view that even pursuit law enforcement vehicles probably don't care for 40 more hp and will like to drink a steady diet of 87 Octane.

Any purported advantageous to a 4.3 or 5.3 liter displacement can largely be equaled with AFM engagement and/or sacrificing some power and torque in favor of a late closing intake cam (a mild Atkinson cam) instead of actually varying the static displacement.

You'll still keep the a pair of DOHC engine lines for displacement tax stricken markets. Not because they are more efficient, or higher performance, but because they are cheaper for owners in those markets to buy and operate. Besides the Super 2.0 V6 will be extremely refined from a vibrational and noise standpoints

• (S1) High Performance Cars (Displacement Restricted) -- V6 Supercharged / Turbocharged, 91 Octane, VVT, DI, VVL, 1998 cc -- 420 bhp @ 6200 rpm / 360 lb-ft @ 2000~6000 rpm
• (S2) Performance Cars (Displacement Restricted) -- I4 Turbocharged, 91 Octane, VVT, DI, VVL, 1998 cc -- 270 bhp @ 6500 rpm / 260 lb-ft @ 1800~5500 rpm
• (S2) Economy Cars (Displacement Restricted) -- I4 Turbocharged / Miller, 87 Octane, VVT, DI, VVL, 1998 cc -- 200 bhp @ 6000 rpm / 180 lb-ft @ 1600~5600 rpm

They should have kept the 2.0T displacement. Simply lower the boost (12 - > 8 psi) and up the compression (10.5:1 --> 11.5:1).

With this we can make a reasonable projection as the the Fuel Economy numbers of an ATS-V if powered by the LT1.

Corvette C6 -----------------------> Camaro SS

3250 lbs ----------------------------> 3850 lbs

Cd 0.34 -----------------------------> Cd 0.35

6.2L LS3 V8 -----------------------> 6.2L LS3 V8

16 (City) / 26 (Hwy) MPG ------> 16 (City) / 24 (Hwy) MPG

Corvette Stingray (C7) --------> ATS-V (Hypothetical)

3200 lbs ----------------------------> 3700 lbs (est)

Cd 0.29 -----------------------------> Cd 0.299

6.2L LT1 V8 (w/ AFM) ----------> 6.2L LT1 V8 (w/ AFM)

17 (City) / 30 (Hwy) MPG -----> 17 (City) / 28 (Hwy) MPG

That's pretty darn good compared even to the naturally aspirated 3.6 DOHC V6 (19 / 28 mpg).

The Corvette Stingray's fuel economy numbers as measure by the official EPA test cycles are...

Corvette Stingray -- 6.2L Pushrod OHV V8 -- 17 (City) / 29 (Highway) MPG*

* 17/28 mpg w/o Cylinder Deactivation; 17/30 mpg in Eco Mode (Enables Cylinder Deactivation)

Compared to the outgoing (C6) model, the 7th Generation Corvette is 1 mpg (city) / 2 mpg (Highway) better in fuel economy without relying on cylinder deactivation. With AFM enabled, this climbs to 1 mpg (city) / 4 mpg (Highway). This is in fact better than an 2009 Acura TL Type-S (17 / 26 mpg) makes the Corvette the most fuel efficient car in its performance category -- certainly the most fuel efficient vehicle with 460 hp / 465 lb-ft and which hits 60 mph in 3.8 secs. For comparison, the fuel economy numbers of some similarly high performing vehicles are as follows:-

Ferrari F458 Italia -- 4.5L DOHC V8 NA -- 12 (City) / 18 (Hwy) MPG

Porsche 911 Turbo -- 3.8L DOHC H-6 Bi-turbo -- 16 (City) / 24 (Hwy) MPG

Nissan GTR -- 3.8L DOHC Bi-turbo V6 -- 16 (City) / 23 (Hwy) MPG

Audi R8 -- 5.2L DOHC V10 NA -- 13 (City) / 19 (Hwy) MPG

Ford Mustang GT500 -- 5.8L DOHC V8 Supercharged -- 15 (City) / 24 (Hwy) MPG

Lexus IS-F -- 5.0 DOHC V8 NA -- 16 (City) / 23 (Hwy) MPG

Lotus Evora -- 3.5L DOHC V6 NA -- 18 (city) / 26 (Hwy) MPG

Get the ATS and CTS right; that's 80% of the pie. They can worry about the S-class segment later. Besides, it doesn't really have to be a brang new platform. It can be a double-stretched Alpha with widened sills.

Well, then leave PSA to the Socialist French Government. If they believe that companies can and should exist to provide jobs and benefits rather than to make profit with jobs and benefits being incidental to that, then let them turn it into a welfare program and let it go down together with Socialist France.

How do you like the Jaguar? I drove a 2009 XF, not supercharged, and it was nice but it feels cramped because of the high belt line. I think even the 09's will be out of my price range, unless it has 90k miles or something, and I don't want that.

Jaguar probably doesn't care about CAFE, but they do care about getting buyers, and I think V8 and Super V8 was overkill for most people. Offering 4 and 6 cylinders gives adequate performance and fuel economy that people want, because 15/23 might turn a lot of people away too.

The turbo 4 is hitting all these luxury cars because an engine like that can make 250-270 lb-ft of torque at a low rpm and with an 8 speed transmission that can get a 0-60 time under 7 seconds which is more than adequate for most. But like Cubical, I still wouldn't want one, I'd want a 6-cylinder at least.

The 2009 has the "old" 4.2 V8. For 2010 through 2012 they had the 5.0 VVT/VVL DI V8s -- both supercharged @ 470~510hp and NA @ 385 hp. The engine is smooth enough and pretty quick revving (for a cross plane V8), but it is a little noisier than the 4.2 due to Direct Injection. Mileage is not bad for the kind of car and engine that they are... 15/21 is actually NOT BAD considering that you are talking about a 4300 lbs car with a 470 or 510 hp engine. The M5 which is in a similar weight and output bracket is 11/17 MPG. For 2013 they added the 2.0T and 3.0 S/C.

The 2013 2.0T is 7.9 secs to 60 mph. I had one as a loaner during warranty service of the XF (audible belt noise / tensioner issue). Driving experience is mixed. It is surprising peppy once it gets in its game or if you keep the revs up above 3000 rpm. The car feels faster than it actually is when driven hard and the I4 is in fact quieter than the V8. The problem with the 2.0T is that at idle or when lugging around at 1500~2000 rpm (which the 8-speed tranny likes to do) stepping on the gas brings a almost 1 sec of slug like acceleration before load builds and the turbo spools enough to get the car moving with enthusiasm. Also, the I4 revs slower than the V8 (even when you just blip the throttle in neutral). With a $3K price difference which covers not just the engine but also additional cabin equipment I'll say the 3.0 S/C is a much better buy. Anyone looking at a $50K car is not going to car much about whether it is 19/30 or 17/28 mpg.

The 2.0T BTW is a Ford engine except for the dress cover. It is the same exact power plant as you will find in the Focus ST or the Fusion in exactly the same tune making the same torque and 2 hp less than Ford's applications mainly due to the XF's quieter exhaust.

The GOV should not be having to think for you and protect yourself from your own lack of common sense and accountability.

Actually, it's not that government should not have to do so. It is that government should not have the right to do so.

This is another example of why Government should take less and do less. I don't need the government forcing backup cameras down my throat or forcing me to pay for one. In fact, getting fixated on a backup camera instead of looking around when backing up is a bad idea. Also, there are other technologies (eg. sky view or sonar sensors) which if backup cameras are mandatory may be displaced -- for cost reasons or because the infotainment screen would have been occupied by back up camera imagery.

Market demand and consumer preference should set equipment standards for automotive frills, not the opinion of some government appointee. From a purely libertarian standpoint, even mandating seat belts and airbags is an over reach -- individuals should have the right to self-endanger by driving without seat belts or buying a car without airbags, as much as they have a right to choose to ride a motorcycle, go surfing or go sky diving (all of which are arguably more dangerous that driving without a seat belt / airbag). But, this backup camera nonsense is getting to the point where government is mandating frills.

Bud the rotary issues are well documented as they have been around for years and you do not have to rehash what everyone already knows. God knows GM figured it out in the 70's.

Second you can use all your so called tech talk that you like to cloud the situation but the fact remains there will be little to no Atkinson engines being developed or in use in the future unless there is a great shift. If it were the way to go there would not be great investments into smaller turbo charged engines by all MFG.

As for the 3.6 TT there no applications yet as they have not gone into production., given time it will show up in more places.

I just find it funny how a guy who argues so much for two valve natural aspiration drives a 32 valve 5.0 SC Jag? I thought you would practice what you preach and stay away from those horrid DOHC.

It's simple... because a Certified Pre-Owned (6yr/100K warrantied) XF S/C was available @ $34.8K with 40K miles. I couldn't find any CTS-V Coupes under $42K (or any C63s for that matter) with that kind of mileage and I am not interested in $5K clutch jobs every 20K miles with the E60 M5. The CTS-V is the preferred option, just not quite as good a deal used.

Fact of the matter is this...

The XF S/C is a 4300 lbs car with 470 bhp / 424 lb-ft and 15/21 MPG (ZF 6-speed auto). This car would have been faster, cheaper, potentially less problematic and have better fuel economy if it had the 460 bhp / 466 lb-ft LT1 Pushrod V8. If not anything, because the engine would be almost 100 lbs lighter and doesn't spend up to 30~40 hp driving the blower. Output is about the same.

The 5.0L AJ133 supercharged engine in the V8 F-type is the same motor as in the XF Supercharged, XFR, XFR-S and XK cars making between 470 and 550 hp (mostly due to bleed valve regulation*). Featuring dual VVT, a cam switching VVL system (2800 rpm switch over from low lift to high lift lobes), direct injection and an Eaton TVS supercharger. It's not a bad engine -- smooth, unexpectedly fast revving (for a X-plane V8) and decent on fuel economy (15/21 mpg; 15/23 mpg on the 8-speed cars). The Ratan Jaguars are also quite reliable compared to the old ones. There is no Lucas anything in there. The engine management systems are largely Ford. From a reliability and cost of ownership standpoint, I'll take an XF, XJ or F-type over any BMW M-car (especially the E60 M5 any day).

In any case, getting 700 hp out of a 5.0 liter blown motor isn't hard. Just don't expect 15/21 mpg when you enlarge the blower, drop the compression and go to a higher rated ZF gear box.

* You can run the XKR-S ECU file on the XF S/C and go from 470 hp to about 520~530, without changing anything else. I know first hand

Most cars get above EPA ratings when you put it on cruise control and drive 30 miles at 65 mph. I get 25.6 MPG on the Jaguar XF Supercharged in that condition even though the EPA rating is 15/21 MPG. This is a 470 bhp / 4300 lbs car with a blown 5.0L V8. BTW, a Corvette C6 is over 30 mpg in that scenario with it's NA Pushrod 6.2L.

That said... most of the time you don't get to drive like that. And, most of the time people are lucky to even match EPA numbers much less exceed them.

Trying to make and sell the perfect Police car is not a bad idea... but trying to go into automobile manufacturing from scratch in this millennium was a leap too far.

The integrated siren lights. The hose washable rear compartment. The suicide doors and plastic body (dent resistant). The integrated dispatch, radio and recording systems. All were great ideas police departments are willing to pay for. But, really, do you really need to build a platform and an automobile from the ground up to have these? Not really.

Carbon should have bought contracted GM or some other existing manufacturer to build a run of custom vehicles on their existing factories and platform. Say an Alpha or a Zeta, with plastic fenders and door panels, with a roof that accomodates built-in (flush) siren lights, get L-3 or Motorola to cough up an integrated dispatch data computer, radio and DVR system. Then sell it. Own no factory, engineer no new platforms. Heck, do it as a equity partnership with an automaker to create a dorminant police car product that will replace the Caprice, Charger and Tauruses -- all of which left much to be desired and are easy targets.

In fact, they already had substantial letters of intent from enough customers to get it started. Trying to buy your own factory and make the cars yourself is simply a poor way to get started!

Here's the fundamental issue...

(1) The ONLY advantage a 4-valve DOHC valvetrain has is that it is able to flow more air and hence produce more power. Everything else about a DOHC valve train is a disadvantage -- four times as many cams, twice as many sprockets and valves, higher friction, bulkier packaging, heavier weights and greater complexity.

(2) In order to capitalize on the ability to flow more air you have to be at high rpms and wide open throttles. At anywhere south of about 4000~5500 rpm depending on the valve lift employed, a 2-valve head is able to achieve 100% volumetric efficiency so the additional flow capacity is moot. At partial throttle, the engine is choked by the throttle butterfly not the valve or intake, so it is also moot. In other words, unless you wind it out a DOHC engine has no advantage.

(3) Between a DOHC engine and a Pushrod engine of the same displacement, the Pushrod engine will have better fuel economy because it has less parasitic frictional losses, it is smaller and it is lighter. However the DOHC engine will be able to maintain its torque output higher into the rev range and hence make more power. You can also use a smaller displacement DOHC engine to equal the pushrod engine's power production. However, because it is smaller in dispalcement it'll make less torque and must be revved higher to achieve the same power output. Lower torque and higher revs before hitting the same power levels is contrary to the duty cycle of trucks.In order to have a similar pulling power, you have to gear it with a lower gearing and lose efficiency.

Let's compare the Dodge Ram and the Silverado...

Dodge Ram 1500 2WD

Engine: 3.6L DOHC 24-valve V6

Transmission: 8-speed Automatic

Output: 305 bhp / 269 lb-ft

0-60 mph: 8.5 secs

Towing Capacity: 6,500 lbs

Fuel Economy: 17 (city) / 25 (hwy) mpg [4x4 = 16 / 23 MPG]

Chevy Silverado 1500 2WD

Engine: 4.3L Pushrod 12-valve V6

Transmission: 6-speed Automatic

Output: 285 bhp / 305 lb-ft

0-60 mph: 7.9 secs

Towing Capacity: 7,200 lbs

Fuel Economy: 18 (city) / 24 (hwy) mpg [4x4 = 17 / 22 MPG]

Even with the significant gearing advantageous of an 8-speed transmission, the DOHC 24v equipped Dodge is out performed and out towed by the Pushrod 12v powered Chevy. Not only that, but it didn't even manage a fuel economy advantage. If both vehicles had the same transmission, the differences would have been even more pronounced.

What does that say about using four cams, four valves per cylinder for performance or downsizing displacement for the sake of fuel economy? Does it really pan out? Not in this case obviously...

The Jaguar XF 2.0 is $47,000, but $50,000 will get you the 340 hp supercharged V6. I don't know if these car companies are putting the 4-cylinders in for CAFE or to keep the price under $50k, or as a way to say $47k gets you the crap engine, so pay $3,000 more for the good one. Perhaps it is all of the above, but I wouldn't want a 4-banger in a mid-level luxury car even if the 8-speed tranny makes it accelerate like a V6.

The only exception I can see is a diesel 4-cylinder because it has loads of torque and possibly 40 mpg, that makes it a sensible buy especially for people that do a lot of highway driving.

Jaguar doesn't care about CAFE, it's a small fine (per car) and they actually itemized it added it to the sticker (really*)! When the XF first came out it had two V8 powerplants -- with or without supercharging -- that's it. It stayed that way from the 2009 through 2011 model year, although the 2010 and 2011 V8s are 5.0L vs 4.2L in the 2009 cars. 2012s actually got a face lift and the new engines but NOT the 8-speed. 2013 brought the 8-speed online. Under Tata, Jaguar has a progressive product upgrade strategy, every year brings something new instead of waiting 4~5 years for a major overhaul of the model.

*I just acquired a 2010 XF Supercharged (5.0L SC w/ 470 bhp) to replace the 2005 C55 AMG... they kept the original window sticker.

The pricing puts it at about $1600~3200 less than an equivalent 5-series. Not out of place as a "sticketr price"

The real question is how much discount GM will end up bribing customers with... nobody pays MSRP... not even for BMWs.

I like your arguments.

You give some accurate facts and mix them with assumptions and sell it all as the truth with no way to prove it.

Then you change the topic in general. I am speaking on engines and all cars in general as the smaller volume of performance is reliant on what engines are available from the higher volume lines.

The only reason you have a LT is because of the trucks. No trucks no V8 engines for anything. It is simple economics. Again you need to factor the whole picture not what just works for you. You can not leave the economic factors out either. Big Picture again!

As for your Atkinson engine it has been around for years and while things like modern supercharging may bring it to a practical option it is far off of being in wide spread use anytime soon. The power density issues are still an issue that have to be overcome. It is efficient but has issue. It is similar to the rotary engine where it has a lot of good but enough bad for wide spread acceptance in the industry.

If this was the way they why has so few really spent much time moving to this. Is it that they understand the issue better than you? I have a hunch the MFG have a little more info and that they have issues to be worked out yet.

And the 3.6 Bi-turbo has "a lot" of applications? How about just two for now -- the XTS and CTS's premium power plant.

Power density is only important if you care about displacement. If you don't it doesn't really matter that much. Let's just say that an Atkinson cammed engine, all else being equal, has a power density about 70~80% that of the conventional Otto cammed counterpart. You'll use a 2.5 liter for similar output as a 1.8 or 2.0 L. The penalty is the additional weight of a 2.5 vs that of a 2.0 or 1.8 which really isn't that much (approximately 10 to 15kg; 22~33 lbs). Quite a small price to pay for about 12~15% gain in fuel efficiency or the equivalent of getting from 32 mpg to 36~37 mpg. You CANNOT match it with by dropping displacement from 2.0 liter to say 1.4 liter and adding a turbocharger. Heck, dropping displacement and adding a turbo often does not even get you better fuel efficiency than the baseline 2.0 liter! Yes, you trade additional weight and space for fuel economy. But then again, so does adding a hybrid drive train. The difference being that going to a larger displacement and using an Atkinson cam costs absolutely nothing financially whereas adding a motor generator, inverter assembly and a big battery pack sets you back several thousands of dollars. A similar argument cam be made for going to a larger displacement while adopting an SOHC 2-valve valvetrain -- except perhaps to a lesser degree.

The rotary is a completely different ball game. The Wankel has three huge problems -- the apex seals run dry unless you burn a pre-mix of oil and gasoline (which sucks for emissions and by design consumes oil), the compression of the mixture is always against the "cold" side of the housing because combustion and exhaust happen elsewhere along the torchoid (this is bad for thermal efficiency because combustion heat is perpetually lost and not recovered) and lastly because the rotary aspirates through ports cut into the sides or the periphery housing making it difficult to implement any kind of variable timing (again bad for emissions and worse for optimizing aspiration to wide range of operating speeds). Rotaries have always have bad fuel economy and worse emissions, and its operating fundamentals make it very hard to address these to the same degree as piston engines. In many ways, it's like trying to make a clean running 2-stroke and giving it a broad power band -- except that it's worse in the thermal efficiency department.

We are not talking about high performance cars in particular. We are talking about the simple fact that "small displacement does not equal low fuel consumption" and consumers by and large don't care how many cams or valves you have on an engine -- most don't even know what a cam is or what a valve looks like. What they the ones who do care about fuel economy look at is that MPG rating on the sticker and what those who care about performance look at is the power figures.

The fact is that if you really want the best MPG numbers -- irrespective of specific output or anything else -- what you will do is first and foremost, go to an Atkinson Cam, then use as few cams, valves and cylinders as you can. Doing so will reduce the output of your engine, so you simply scale up the displacement to recover the lost power. This is a more effective approach than scaling down displacement and piling on a turbocharger or two.

MY FACTS

FACT: Cruze 1.4T 6AT @138hp = 26/38 mpg vs Focus 2.0 @ 160hp = 27/38 mpg

FACT: Camaro SS 6.2 Pushrod @ 400hp = 16/25 mpg vs Taurus SHO 3.5TT @ 365 hp = 17/25 mpg vs M3 4.0 DOHC V8 @ 414 hp = 14/20 mpg vs Lexus IS-F 416 @ hp = 16/23 mpg

FACT: Corvette Stingray 6.2 @ 460 hp >= 17/27 mpg vs Porsche 911 GT3 @ 475 hp = 14/21 mpg

YOUR SECULATIONS

SPECULATION: Consumers prefer smaller engines regardless of fuel economy numbers

SPECULATION: Consumers prefers DOHC valvetrain (or even know what that is) over performance

SPECULATION: Consumers prefer a Twin Turbo V6 car even though it is slower, less fuel efficient and more expensive.

I already did... and all you are able to say is something along the lines of "everybody says the world is flat, so it must be."

Amen to dropping the 2.5 liter. 2.0T is a good base engine. Agreed that if they ask a premium price, you have to have a premium product.

As far as turbo V6's the Nissan GT-R does fine with what it has, in pretty much beats every V8 and V12 in 0-60 sprints. But I still think once BMW said the M3 would have 6 cylinders, Cadillac made it's mind on 6 cylinders. BMW decides what the market wants, and Cadillac is going for the Euro-Import buyer that BMW, Audi and Porsche already have groomed to shop a certain way. If that crowd wanted big V8s, they would buy the Corvette over the Boxter or an SRT8 Charger over an S4 or 335i, etc. Even Mercedes and Jaguar who used to love V8s are moving away from them to use more V6s.

The reality is everything is going to get smaller and while the V8 may be around it will get more and more expensive to drive people to smaller engines.

Europe and out side the USA the V8 is not a must have default as most of these countries have been paying much higher fuel prices for much longer, most have never even had a V8 in the family for several generations. Also the Green movement in places like Europe have an affect on the market.

In the State the V8 was the default for 80% of the buyers but in cars today it is becoming a are item. Even the V6 is no where as common as it once was. The last two generations have grown up in cars with 4 cylinder engines and they expect the same. Even many who have a V8 in the 80's in the family only had a V8 with just under or at 200 HP while today most 4 cylinders will do that even without a turbo.

The fact is it will be difficult to meet the coming CAFE standard even with small 4 cylinder car let alone larger cars with even larger engines. That is why we are seeing the goofy Hybrid systems that they hope will develop to give them room for larger cars. The V8 will remain longer but GM and others will limit it's use to models that have lower standards like heavier trucks and use loop holes of the larger trucks to still over them. As for cars like the SS they will price them high and you can have one but the price will limit the sales naturally for the MFG.

Europe just has a whole different outlook than the states at engines and even here it has evolved an continues to do so.

The kink with that argument is that the assumption that a 6.2 liter Pushrod V8 consumes more fuel than a 3.6 Liter Bi-turbo V6 is in general not true. The only thing that dings the V8 is the large displacement incurring higher displacement taxes in those countries that have them. As far as MPG ratings is concerned, a Pushrod V8 is exemplary, matching beating DOHC V8s and force fed V6es of equivalent power output any day.

As far as the ATS-V is concerned, a 6.2 LT1 V8 will post MPG numbers better than 16 (city) /25 (hwy) MPG -- 16 /25 is achieved by a Camaro SS 6 speed-Auto using the previous generation Port Injected 6.2 V8. In other words, the V8 -- if employed -- will be 17 (city) / 26 (Hwy) or better, unless all the VVT, AFM and DI stuff they did amounted to no improvement in mileage numbers (one of the major engineering goals). Given that the 3.6 NA engine which has higher compression, resonance tuned intakes and freer flowing exhaust came in at 19 (city) / 28 (Hwy) it'll be very difficult for a 3.6 TT to beat 17/26 MPG. I don't think you fully comprehend the advantageous of a Pushrod valvetrain -- in addition to making the engine lighter and more compact, it is also somewhat more fuel efficient than a DOHC design (definitely so at the same displacement and still modestly so at the same output with a larger displacement).

The argument that going to smaller 4-cyliner engines equates to better mileage number is also for the most parts unproven at best. The 1.4L Turbo Cruze did not beat its 1.8 and 2.0L NA competitors (with similar or higher power ratings) in mileage numbers. In fact, it lost to the majority of these cars. If you really wanted the "best" mileage numbers than a 2.0 DOHC 16v DI four you are better off going BIGGER in displacement, dropping cams and ditching valves! Go to 2.5 or 2.7 liters, go to a SOHC head, go to 2-valves per cylinder and most importantly go to an Atkinson cam. Do that and you'll run circles around the 2.0L DOHC16v engine in MPG numbers while generating similar output. Even if you don't go atkinson cammed, just going to 2.3L, dropping one camshaft and dropping halve the valves will see an improvement in MPG numbers. Specific output goes down the drain... but we are after the best fuel economy here not bragging rights about hp/liter.